1. Background of the Invention
Among crystal oscillators, VC-TCXO (Voltage Controlled-Temperature Compensated Crystal Oscillators) compensate the frequency temperature characteristics of crystal resonators, and for example, maintain the oscillation frequency at a nominal value (nominal frequency) by means of a voltage from an AFC circuit. As a result they are applied as frequency reference sources in communication devices such as mobile phones, which follow environmental changes. In recent years, user demand has diversified, and for example, with regard to mobile phones, there is a multifunctional temperature compensated crystal oscillator in which; a reference signal source for a PLL having an operation/non-operation function (ON/OFF of an oscillator output), and an output terminal serving as a block signal source, are provided discretely.
2. Prior Art
FIG. 5 illustrates a conventional example of a crystal oscillator (VC-TCXO), wherein FIG. 5A is a cross-sectional view thereof, FIG. 5B is a plan view of the inside bottom surface of the chamber body thereof viewed excluding the cover, and FIG. 5C is a plan view of the outside bottom surface thereof.
This crystal oscillator, for example, as shown in FIG. 5A, accommodates an IC chip 2 and a crystal blank 3 within a concave-shaped cross-section chamber body 1 composed of a laminated ceramic, and is hermetically sealed by joining a metal cover 4 to the top end surface of the chamber body 1. The chamber body 1 has; a pair of crystal holding terminals 5 at an inside wall stepped portion of the concave portion, circuit terminals 6 on the inside bottom surface 1a thereof, and mounting terminals 7 on the outside bottom surface 1b. The crystal holding terminals 5 are electrically connected to crystal terminals of the circuit terminals 6, and furthermore, the circuit terminals 6, excluding the crystal terminals, are electrically connected to the mounting terminals 7 provided on the outside bottom surface 1b by means of conductive paths including through electrodes (not shown in the figure). The IC chip 2 is fixed to the inside bottom surface 1a of the chamber body 1 by ultrasound thermocompression bonding using a bump (not shown in the figure) for example (so-called “flip-chip bonding”).
As shown in FIG. 6, the crystal blank 3 has excitation electrodes 8a on both principal surfaces thereof, and lead-out electrodes 8b extend to both sides of one end. As shown in FIG. 5A, both sides of one end of the crystal blank 3 from which the lead-out electrodes 8b extend, are fixed to the crystal holding terminals 5 provided on the inside wall stepped portion by an electrically conductive adhesive 9. Furthermore, the metal cover 4 is joined by seam welding, for example, to a metal ring (not shown in the figure) provided at the open end surface of the chamber body 1 so as to hermetically seal the crystal blank 3 and the IC chip 2 within the chamber body 1. In a state in which the crystal blank 3 is hermetically sealed, these are referred to as a crystal resonator or a crystal unit.
(Basic Circuit Configuration)
The basic circuit configuration of a conventional VC-TCXO shown in FIG. 7 is one that is integrated within the IC chip 2 shown in FIG. 5A, and has a voltage controlled oscillation circuit and a temperature compensating device (not shown in the figure). That is to say, it has basic functions of a first oscillator output function, wherein the oscillation frequency is controlled by a control voltage, and a temperature compensating function. The oscillation circuit is formed together with an external crystal resonator (crystal blank 3), and is made a voltage controlled type by inserting into an oscillation closed loop, a voltage variable capacitative element (not shown in the figure) such as a varicap diode, to which the control voltage is applied. The control voltage is an automatic frequency control (AFC) voltage from an AFC circuit for example, and this is applied to the voltage variable capacitative element and matched with the nominal frequency.
As shown in FIG. 7, the temperature compensating device includes, at the very least, a temperature sensor 11 which is a linear resistance for example, that detects ambient temperature, and generates a detection voltage corresponding to the ambient temperature. The resulting temperature compensation voltage is, for example, applied to the aforementioned voltage variable capacitative element. Furthermore, in particular, changes in the oscillation frequency originating from the frequency temperature characteristics of the crystal resonator are offset by this voltage, to compensate the temperature.
The temperature compensation voltage is supplied at all times during operation of the oscillation circuit, and the AFC voltage is supplied when necessary from the AFC circuit built-in to mobile phones in which the crystal oscillator is installed. Furthermore, the temperature compensation data for the temperature compensating device is written using the mounting terminals 7 (Vcc, Vout, GND, Vafc) shown in FIG. 5C, which have a basic function. Moreover, the mounting terminals 7 which have a basic function, are disposed in a clockwise direction starting with the upper left diagonal shown in FIG. 5C in the order of, for example, power supply, first oscillator output, earth, control voltage, and AFC input terminals (Vcc, Vout, GND, Vafc).
(Multifunctionalization of the VC-TCXO)
Furthermore, in a case where the VC-TCXO is made multifunctional, as shown in FIG. 7, the oscillator output of the VC-TCXO is branched in parallel for example, and is made a first output Vout1 and a second oscillator output Vout2 via first and second buffer amplifiers 12a and 12b. The buffer amplifiers 12 prevent waveform distortions or the like, resulting from mutual interference between the first and second oscillator outputs Vout1 and Vout2.
Here, the first and second oscillator outputs Vout1 and Vout2 are both clipped sine waves. The first oscillator output Vout1 is a normal standard signal source of a synthesizer from a PLL for when the received frequency is made an intermediate frequency for example. Furthermore, the second oscillator output Vout2 is a baseband clock source serving as a continuous output. An operation/non-operation signal (Ved) corresponding to the intermittent operation of the PLL circuit is applied to the first buffer amplifier 12a for example, and it has an operation/non-operation function that turns the first oscillator output Vout1 ON/OFF. The operation/non-operation signal is applied to the base of the first buffer amplifier 12a or to the switch of the power lines. Furthermore, the operation/non-operation function corresponds to a standby function in a clock oscillator, and has an object in power savings.
In addition, the detected temperature voltage from the temperature sensor 11 of the temperature compensating device shown in FIG. 7 is output as temperature data, and is utilized as necessary for temperature compensation of external circuits for example. As a result, additional functions, namely a second oscillator output function, an operation/non-operation function, and a temperature voltage output function, are added to the basic functions of the VC-TCXO.
Due to this, on one principal surface (circuit formation surface) of the IC chip 2, as shown in FIG. 8A, there is provided as IC terminals 13, in addition to basic IC terminals 13a, namely crystal terminals X1 and X2, the power terminal Vcc, the first oscillator output terminal Vout1, the AFC input terminal Vafc, and the earth terminal GND, additional IC terminals 13b, namely the second oscillator output terminal Vout2, an operation/non-operation input terminal Ved, and a temperature output terminal Vtsens, to give a total of nine terminals. As shown in FIG. 8B, the terminals are provided on both sides along the length direction of the IC chip 2, and a dummy terminal (NC) that maintains the symmetry is provided to give a total of ten terminals.
In FIGS. 8A and 8B, the reference symbols 13a and 13b of the basic IC terminals and the additional IC terminals are conveniently omitted, and all of the IC terminals are denoted by reference symbol 13. Furthermore, the corresponding basic and additional mounting terminals 7a and 7b, and additionally, the basic and additional IC intermediate terminals 13a′ and 13b′ are omitted to illustrate from FIGS. 8A and 8B, and the mounting terminals and the IC intermediate terminals are denoted by reference symbols 7 and 13′, respectively, in the present specification.
The aforementioned circuit terminals 6 formed on the inside bottom surface 1a of the chamber body 1 are formed corresponding to these IC terminals 13. Furthermore, except for the crystal terminals X1 and X2 shown in FIG. 7, they are electrically connected to the mounting terminals 7 provided on the outside bottom surface lb of the chamber body 1 by means of a wiring path (circuit pattern) including through electrodes (through holes), or the like. However, there are two earth electrodes GND among the mounting terminals 7 to give a total of eight terminals, and the symmetry is maintained.    [Patent Document 1] Japanese Unexamined Patent Publication No. 2003-324318    [Non-Patent Document 1] Miniature Surface Mounted VC-TCXO Module (Model Name: DSA222MAA) Catalog published by Daishinku Corp.